The invention is directed to a fire-resistant ceiling element for an industrial furnace, a ceiling for an industrial furnace made of ceiling elements as well as an industrial furnace with such a ceiling.
Different ceilings for industrial furnaces are known. One possibility is the construction of a ceiling in the shape of an arch. In most cases circular curve arches are used. The arch is then constructed of radial stones of commercial format.
The arches can for example consist of silicon or fire clay stones. The stability of such arch constructions is limited though, since crystal modifications in fire clay stones, for example, cause changes in volume under exposure to different temperatures.
Arch constructions are used, for example, for glass tanks or Siemens-Martin-furnaces.
Particularly for greater arch spans arch constructions are not useable. In these cases so-called hanging ceilings are installed, which are also made of fire-resistant stones sustained in a hanging position by a steel construction, which is not exposed to high temperature changes. There are a number of different variations of such hanging ceilings (for example in the German Disclosure Document No. 18 15 687). One advantage of the hanging ceilings is that the shape can be flexible. Consequently, level hanging ceilings are also possible.
Depending on the temperature requirement the stones for such hanging ceilings are made of different fire-resistant qualities.
The hanging ceilings exhibit many disadvantages as well.
Since they are composed of a great number of individual stones which, moreover, must be anchored in a steel construction, the assembly requirements are great. Such walls, moreover, are very heavy. When heating the furnace, the big ceiling mass is heated as well, sometimes leading to the requirement of extremely higher energy loads. A use of this construction in periodically operated furnaces, i.e., in firms where the furnaces are to be turned off over the weekends or on holidays, leads to volume expansions and contractions in the fire-resistant stones, caused by the constant heating and cooling process. Moreover, tensions build up, leading to cracks. Falling individual particles or crystals of the fire-resistant ceiling stones cannot always be avoided.
Especially when using such industrial furnaces for delicate firing material, damage caused by falling debris occurs often. When firing sanitary ceramics, for example, falling particles of the fire-resistant materials landing on the glaze can make the finished glazed product worthless.
Once these hanging ceilings sustain greater damage, their repair is very complicated since the damaged areas are hard to reach without turning off the furnace.
The anchoring of the fire-resistant stones in a metallic frame, finally, is also problematic, not only because the two materials have different heat expansion coefficients, but also because the fire-resistant materials can be exposed to corrosion through the metal anchor and the insulation of the ceiling as such is cut off at the point of those metal suspensions. From the German Utility Model No. 18 32 912 a ceiling element is known, which consists of a reinforced tamping clay. This makes the ceiling element heavier, and under exposure to higher temperatures problems arise, since the heat expansion coefficients in reinforcing and fire-resistant materials differ.